On tidal capture of primordial black holes by neutron stars

The fraction of primordial black holes (PBHs) of masses $10^{17} - 10^{26}$ g in the total amount of dark matter may be constrained by considering their capture by neutron stars (NSs), which leads to the rapid destruction of the latter. The constraints depend crucially on the capture rate which, in turn, is determined by the energy loss by a PBH passing through a NS. Two alternative approaches to estimate the energy loss have been used in the literature: the one based on the dynamical friction mechanism, and another on tidal deformations of the NS by the PBH. The second mechanism was claimed to be more efficient by several orders of magnitude due to the excitation of particular oscillation modes reminiscent of the surface waves. We address this disagreement by considering a simple analytically solvable model that consists of a flat incompressible fluid in an external gravitational field. In this model, we calculate the energy loss by a PBH traversing the fluid surface. We find that the excitation of modes with the propagation velocity smaller than that of PBH is suppressed, which implies that in a realistic situation of a supersonic PBH the large contributions from the surface waves are absent and the above two approaches lead to consistent expressions for the energy loss.Comment: 7 page

Le chiasme, notamment chez Albert Camus

R. Bernard Pingaud écrivait récemment : « en décembre 1959, interrogé par un journaliste américain qui lui demandait ce que la critique avait négligé dans son œuvre. Camus répondait : « la part obscure, ce qu’il y a d’aveugle et d’instinct en moi »... Là est sans doute la clé de son pouvoir, dans cette part obscure qui exige qu’on l’interprète et qui résiste à toutes les interprétations ». Résistera-t-elle, cette part inconsciente, à ce que la grande rhétorique poétique grecque nous a confié ..

A damage model for transversely isotropic materials

International audienceIn a nuclear disposal project, the damage of the hosting rock is a capital issue that should be studied and understood. This problem is even more complex when the studied rock is anisotropic. In the present paper, a damage model that takes into account both initial and induced anisotropy is introduced using equivalence relations between the real material and a fictitious isotropic one on which we can take all the advantages of the well established isotropic theory. Numerical simulations using a Finite Element Method (FEM) code shows an agreement between the theoretical predictions and the experimental data of Brazilian tests with different orientation angles

A multidisciplinary study of a syntectonic pluton close to a major lithospheric-scale fault: relationships between the Montmarault granitic massif and the Sillon Houiller Fault in the Variscan French Massif Central. Part II: Gravity, aeromagnetic investigations and 3D geologic modeling.

International audienceNew gravity and aeromagnetic investigations have been carried out to understand the emplacement mechanisms of a granitic pluton and the relationships with a nearby lithospheric-scale fault. This paper concerns the second part of a methodological multidisciplinary study and complements previous geochronologic and Anisotropy of Magnetic Susceptibility (AMS) studies on the same pluton. In the northern part of the Variscan French Massif Central (FMC), the Montmarault massif crops out along the Sillon Houiller Fault (SHF). Bouguer and aeromagnetic anomaly maps imply thickening of the pluton along the SHF and suggest laccolitic spreading northwestwards. Based on petrophysical measurements, direct 2D joint gravity and magnetic modeling has been performed along 10 cross-sections. In order to quantitatively constrain the 3D pluton geometry and its relationships with surrounding geologic units, these geophysical cross-sections, new structural information (field and AMS measurements) and petrophysical data have been integrated into a regional 3D geological and geophysical model. Altogether, the results obtained from geochronology, petro-magnetic fabrics (Part I), gravity and aeromagnetic investigations as well as 3D modeling (Part II), demonstrate that the Montmarault pluton was emplaced during the Namurian period along the SHF. Our results further show that, at that time, in response to a NW-SE regional extension, if the SHF existed, it behaved as a normal fault. Mylonites attesting for synmagmatic normal motion on the northeastern part of the Montmarault pluton strengthen this tectonic scheme. During the Late Carboniferous, the FMC experienced NE-SW extension along the SHF by 80 km of brittle left lateral wrench offset. This second tectonic event is well recorded in the Stephanian coal basins which were formed along NW- SE listric brittle faults and constrain the present-day shape of the Montmarault pluton

Les séismes du Frioul de 1976 : étude de la région focale

Le plan de notre travail se présentera de la façon suivante : dans une première partie, à partir des spectres d'amplitude des ondes P, nous étudierons les paramètres des sources associées aux séismes proches et le facteur de qualité dans la zone focale. Nous décrirons préalablement les méthodes expérimentales de calcul de ces divers paramètres. Puis, dans la deuxième partie, nous montrerons l'existence d'une dispersion différentielle dans la région focale. Cette notion sera développée et une méthode de calcul numérique de ce paramètre sera définie . Les résultats expérimentaux seront discutés à partir de l' hypothèse suivante: la dispersion observée est la conséquence de l'atténuation.pas de résum

Etude et caractérisation des structures hercyniennes à partir de données sismologiques (le cas du massif armoricain)

STRASBOURG-Sc. et Techniques (674822102) / SudocPARIS-BIUSJ-Sci.Terre recherche (751052114) / SudocSudocFranceF